Studies of human color vision suggest that much of the data on detection and discrimination of color stimuli can be explained with only three independent cardinal mechanisms, tuned to different directions in color space, and a summation rule such as probability summation. Recent studies suggest that higher order color mechanisms, tuned to many different directions in color space, may influence detection and discrimination of color stimuli under some conditions. The action of higher order color mechanisms has been revealed most clearly by changes in the adaptive state of the observer. These higher order color mechanisms presumably combine signals from the three cardinal mechanisms which are believed to be formed in the initial stages of the visual system. Two aims of the proposed work are to determine whether cardinal mechanisms function independently in chromatic search tasks and whether higher order color mechanisms, tuned to many different directions in color space, contribute to the detection of a target stimulus in chromatic search tasks. Studies of visual search tasks have suggested that a somewhat different, more flexible, type of higher order mechanism under attentional control may contribute to the detection of a target stimulus among heterogeneous distractor stimuli. Results from these studies suggest that signals in different sensory coding mechanisms may be combined in mechanisms under attentional control to facilitate detection of the target. The sensory signals to be combined can be selected by the observer and may vary from task to task. The third aim of the proposed work is to investigate how signals in different color mechanisms are combined in mechanisms under attentional control to facilitate the detection of a target stimulus among distractor stimuli that are heterogeneous in color.